Porcellanite


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porcellanite

[pȯr′sel·ə‚nīt]
(petrology)
A hard, dense siliceous rock, such as impure chert or indurated clay or shale.

Porcellanite

 

clays, argillaceous schists, clay marls, and other rocks altered through the action of underground fires in coal seams into dense, porcelaneous rocks, which may be white, pink, mottled, or dark. Porcellanite also contains mullite, cordierite, wollastonite, and other minerals. It is formed at temperatures reaching 1,300°C. Porcellanite is also formed when waste piles burn and sometimes assumes a slaglike appearance.

Porcellanite is used as a building material, namely ballast; when pulverized, it acquires binding properties and is used as a cement additive. In the USSR, it is mined in the Angren River valley in Uzbekistan, where kaolin clays between coal seams have been altered. The term “porcellanite” is common in the United States, where it is applied to an impure variety of a siliceous rock, usually opalescent, that has the texture and luster of unglazed porcelain.

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Table 2 Sites excavated at Hope Inlet Site Site type Length Width Depth Dominant (m) (m) (m) component HI2 Shell mound 22 20 0.4 Anadara HI6 Earth mound 18 8 1.0 earth HI66 Sub-surface 30 30 0.6 Anadara midden HI80 Shell mound 10 6 1.2 Anadara HI81 Shell mound 15 14 1.6 Anadara HI83 Shell mound 16 14 1.0 Anadara HI97 Earth mound 14 12 0.7 earth Site Stone Environmental artefacts context HI2 hinterland margin adjacent to saltflats HI6 porcellanite flakes inland HI66 tuff flake hinterland margin adjacent to swamp HI80 saltflats HI81 quartz flakes hinterland margin adjacent to saltflats HI83 quartz flakes inland quartzite pestle HI97 quartz flakes hinterland quartzite mortar margin adjacent to saltflats
Other cultural material observed includes charcoal, bone and the very occasional stone artefact, except in site HI6, which contained numerous flakes throughout the deposit, manufactured from porcellanite, as well as white ochre.
The excavations revealed a low density of stone artefacts in all but the earth mound site (HI6), which contained only unspecialised flakes manufactured from a locally occurring porcellanite. The limited number and type of stone artefacts and raw materials within the mounds is in sharp contrast to the variety of artefact types and exotic raw materials found in the stone artefact scatters on the surface of the saltflats.